The solar cell industry is divided into the first generation solar cell, the second generation solar cell, and the third generation solar cell in consideration of a fabricating cost and efficiency of a solar cell. The first generation solar cell, which is a crystalline silicon solar cell that has been developed for decades, currently accounts for 80% or more of all solar cells. The second generation solar cell, which is a solar cell for supplementing a disadvantage of a silicon solar cell having high efficiency but also having a high fabricating cost, means a thin film such as amorphous silicon, a compound, an organic thin film, and the like, and the third generation solar cell, which is a solar cell for obtaining high efficiency at a low cost, means a new solar cell utilizing a nanostructure and a quantum dot.
Since the silicon solar cell, which is the first generation solar cell, has reached the technical limits, research and development for the second generation thin film solar cell has mainly been actively conducted. However, in order to rapidly reach grid parity of a solar cell, development of the low cost and high efficiency third generation solar cell has been demanded.
As one of the promising third generation solar cells, a silicon quantum dot solar cell has been suggested. In this silicon quantum dot solar cell, theoretically, high efficiencies of 29% and 47.5% are expected in the single junction and triple junction solar cells, respectively.
However, the actual efficiency has not approached this theoretical efficiency at all up to now, such that research into finding a cause thereof has been actively conducted.
One of the main reasons that the high efficiency is difficult to be obtained is the low electrical conductivity of the silicon quantum dot layer where the Si quantum dots are enclosed by dielectric medium, such as, SiO2, Si3N4, and so on. Therefore, the efficiency of the Si quantum dot solar cell is low because of the use of a thin light absorbing layer.
The present applicant has suggested a new structure of a photo active layer that allows electrical conductivity not to be decreased even though a thickness of a light absorbing layer is increased and that may be fabricated in a thick film form, as a result of concentrated research into a quantum dot based solar cell in order to solve the above-mentioned problem.